1. Field of the Invention
The present invention relates to a semiconductor apparatus on which elements or semiconductor chips are mounted, and also relates to a method of fabricating the apparatus.
2. Description of the Related Art
With portable electronic appliances such as mobile phones, PDAs, DVCs and DSCs becoming more and more advanced in their capabilities, miniaturization and weight reduction of products have become essential for market acceptance. Accordingly, highly-integrated system LSIs for achieving these goals are demanded. Also, better ease and convenience of use are required of these electronic appliances. In this respect, high capabilities and high performance are required of LSIs used in these appliances. While the number of I/Os is increasing as a result of increasingly high integration of LSI chips, there is also a persistent requirement for miniaturization of packages themselves. In order to meet these incompatible demands, development of a semiconductor package adapted for high-density substrate mounting of semiconductor components is in serious demand.
Ball grid array (BGA) is known as an example of package adapted for a demand for high density. A BGA is formed such that semiconductor chips are mounted on a package substrate and then molded by resin. Solder balls are formed as terminals in selected areas on the opposite side. In BGA, an uninterrupted mounting area is secured so that miniaturization of a package is achieved relatively easily. The circuit board need not be adapted for small pitch and a high-precision mounting technology is not necessary. Therefore, by using BGA, the total mounting cost may become reduced even if the package cost is relatively high.
FIG. 6 is a schematic illustration of the structure of a BGA generally used. The BGA 100 is constructed such that an LSI chip 102 is mounted on a glass epoxy substrate 106 via an adhesive layer 108. The LSI chip 102 is molded by sealing resin 110. The LSI chip 102 and the glass epoxy substrate 106 are electrically connected by a metal wire 104. On the back surface of the glass epoxy substrate 106 are arranged solder balls 112 in arrays. The BGA 100 is mounted on a printed circuit board via the solder balls 112. In the technology for mounting elements on the substrate and sealing the elements, it is important to ensure satisfactory adhesion between the substrate and the sealing resin and between the elements and the sealing resin.
A method of building a stack of semiconductor chips is known as a technology adapted for a demand for high density (see the patent document No. 1). FIG. 7 illustrates the structure of a chip size package (CSP) described in the above-mentioned document. A semiconductor chip 1 is mounted on an insulating substrate 3 provided with an interconnect layer 4 on its surface, with the circuit facing upward. A semiconductor chip 2 is mounted on the semiconductor chip 1 via a thermal adhesion sheet 7. The semiconductor chips 1 and 2 and an electrode part of the interconnect layer 4 are connected to each other by a wire 8. The semiconductor chips 1 and 2 and the wire 8 are sealed by resin.
When semiconductor chips are build in layers, however, satisfactory adhesion between the semiconductor chips built in layers is not ensured, causing the reliability of elements to become poor and the yield in element fabrication process to drop. When building layers of semiconductor chips, it is important to ensure satisfactory adhesion between the semiconductor elements built in layers. When adhesion at the interface is poor, the elements are affected by thermal stress and humidity, causing the reliability of elements to become poor.    Related Document No. 1    Japanese Published Patent Application No. 11-204720